1. Field of the Invention
This specification relates to an electromagnetic switch capable of switching on or off high voltage direct-current (DC) power.
2. Background of the Invention
An electromagnetic switch is an apparatus equipped for controlling power supply to lines. The electromagnetic switch is widely being used for home appliances as well as for industrial goods. In recent time, as electric vehicles, such as hybrid vehicles, fuel cell vehicles, golf cart and the like, are widely developed, the electromagnetic switch is being applied, as a DC power switch, to the electric vehicles.
The electromagnetic switch generates arc upon blocking DC power of high voltage. The arc is controlled by permanent magnets located near stationary electrodes and a movable cotact arm, thereby minimizing (preventing) damages, caused due to the arc, on an arc-extinguishing unit and a driving unit of the electromagnetic switch.
FIG. 1 is a sectional view of an electromagnetic switch according to the related art. As shown in FIG. 1, the related art electromagnetic switch includes a magnetic driving unit fixed to an inside of an outer case 30, which has stationary electrodes 18, so as to apply a magnetic force for driving a movable unit to be explained later, a movable unit movably installed in the outer case 30 for switching power on or off by selectively contacting the stationary electrodes 18 while being moved up and down by the magnetic driving unit, a gas sealing unit located near an upper portion of the movable unit to form an extinguishing chamber 20 for sealing arc-extinguishing gas of the electromagnetic switch.
The magnetic driving unit includes an excitation winding 11 magnetized when current is supplied while demagnetized when current supply is blocked so as to generate a magnetic pull (attractive force), an upper yoke 12 installed above the excitation winding 11, a lower yoke contacting the upper yoke 12 to cover an outer circumferential surface and a lower side of the excitation winding 11, a stationary core 14 wrapped by the excitation winding 11 and fixed to the inside of the outer case 30, and a movable core 15 installed at one side of the stationary core 14 in an axial direction, wrapped by the excitation winding 11 and movably installed within the outer case 30. A return spring 25 may be located between the stationary core 14 and the movable core 15 to apply an elastic force to the movable core 15 such that the movable core 15 can return to its original position, namely, a position spaced apart from the stationary core 14 when the excitation winding 11 is demagnetized.
The movable unit includes a shaft 16 coupled to the movable core 15 to be movable up and down, and a movable cotact arm 17 located at an upper end of the shaft 16 to form electric contact points with the stationary electrodes 18. A wipe spring 26 may be installed between the movable cotact arm 17 and the upper yoke 12 to maintain contact pressure between the movable cotact arm 17 and the stationary electrodes 18 at an ON position of the electromagnetic switch, at which the movable cotact arm 17 contacts the stationary electrodes 18.
The gas sealing unit includes an insulating member 22 formed in a tube-like shape, a hermetic member 23 formed in a tube-like shape to hermetically seal a space between the insulating member 22 and the upper yoke 12, which will be explained in detail later, and a hermetic cap 24 hermetically surrounding the movable core 15 and the stationary core 14.
An unexplained reference numeral 21 denotes a bobbin, which is wound by the excitation winding 11 and supports the excitation winding 11.
Operations of the related art electromagnetic switch having such configuration will briefly be described.
When the excitation winding 11 is magnetized by current supply, a magnetic flux generated from the excitation winding 11 moves along a flow path of the magnetic flux, which is defined sequentially by the movable core 15, the stationary core 14, the upper yoke 12 and the lower yoke 13, thereby forming a closed circuit of the magnetic flux. Accordingly, the movable core 15 linearly moves up to come in contact with the stationary core 14, and simultaneously the shaft 16, which is coupled to the movable core 15 to be movable together with the movable core 15, moves upwardly. The movable cotact arm 17 installed at the upper end of the shaft 16 then comes in contact with the stationary electrodes 18, consequently, a DC power source side and a load side are connected such that the electromagnetic switch can be in an ON state for allowing DC power supply.
On the other hand, when the current supplied to the excitation winding 11 is blocked, the excitation winding 11 is demagnetized, and accordingly, the movable core 15 moves back to the lower side, namely, the original position spaced from the stationary core 14, by the return spring 25. The shaft, which is connected to the movable core 15 to be movable together with the movable core 15, moves downwardly as well. The movable cotact arm 17 installed at the upper end of the shaft 16 is then separated from the stationary electrode 18 to disconnect the DC power side from the load side, such that the electromagnetic switch can be in an OFF state of blocking the DC power supply.
Here, as shown in FIG. 2, at the moment when the movable cotact arm 17 is separated from the stationary electrodes 18, arc A is generated between the movable cotact arm 17 and the stationary electrodes 18, and an expanded length and a lasting time of the arc become different according to magnitudes (levels) of voltage and current. In some cases, the expanded arc may occupy partial regions of the upper yoke 12 and the shaft 16, thereby causing damages thereon.
However, since the related art electromagnetic switch is not equipped with an arc protection device between the upper yoke 12 and the shaft 16, high voltage impulses or debris between contacts, which are generated together with the arc, may cause internal components of the electromagnetic switch, such as the upper yoke 12 and the shaft 16, to be damaged.